1. Field of the Invention
The present invention is in the field of audio processing and audiometry. More particularly, the present invention is in the field of enhancement of audio signals based on a particular user's hearing acuity profile.
2. Discussion of the State of the Art
Audiometry is used to test an individual's hearing ability, or acuity, and is normally performed by a professional audiologist. Typically, a device called an audiometer is used to determine a test subject's hearing levels. The test is designed to determine the threshold of audibility or the level of sound just audible to the test subject listener. This is a behavioral test in that the test subject must cooperate by listening carefully and signaling that the frequency played has been heard. Instructions are given concerning the test procedure, requiring the test subject to indicate the moment at which he can just hear or not hear a specific sound. Normally the test subject is asked to click a button or wave a hand as soon as the sound level becomes audible to him. Thus the lowest intensity sound they hear is recorded. Typically the ears are tested individually using earphones in an environment free from background noise. Both of the test subject's ears are tested through a range of frequencies, for example 0.5, 1, 2, 3, 4, 6, and 8 kHz. The hearing threshold is recorded for each frequency via a series of sound exposures with increasing volume. The technique enables a comparison of the individual's threshold of hearing at each frequency with a reference value. Another common set of frequencies used uses a series of frequencies an octave apart from each other, namely 125, 250, 500, 1000, 2000, 4000, 8000 Hz. From this data an audiogram or pictorial representation of hearing loss at various frequencies is produced.
The audiogram is a standard way of representing a person's hearing loss. Standard audiograms cover a limited range of around 100 Hz to 8000 Hz and plot the threshold of hearing relative to a standardized curve that represents “normal” hearing. Ideally the audiogram, when plotted, would be a straight line, but in practice everyone is slightly different and small variations are considered normal.
While the human ear is capable of resolving around 1500 frequencies, standard audiometry protocols typically involve tests of only six to eight frequencies, and are usually focused primarily on detecting significant hearing loss and allowing medical professionals to compensate sufficiently that the hearer is able to perceive speech reasonably well. This limitation in the art arose when technologies were less capable than today, and when restoring the ability to communicate well with others was as much as could be expected with available hearing aids. However, even people who are not diagnosed as “hearing impaired” will typically, over their lives, develop variations in hearing acuity that may interfere, for example, with their enjoyment of music. Testing only at six or eight frequencies will generally be effective in detecting medically significant hearing loss due, for example, to pathologies of the ear or brain, but they will not detect individual frequencies that have developed lower acuity than an individual's overall level. This can happen when a person is exposed, especially on a repeated basis, to exceedingly high levels of noise at a particular frequency (for instance, if a person works for years in the presence of machinery that gives off strong narrowband sound, especially if adequate hearing protection is not routinely used). Normally variations in hearing acuity are expected in individuals who are not considered to be suffering from hearing loss. It generally is not practical for an audiologist to test all available frequencies, and accordingly most audiometric standards, equipment, and protocols—and most hearing aids—are designed to test for, and compensate for, only hearing loss on a few standard frequencies. For these reasons, the audiometric standards in the art today are not suitable for assisting individuals, whether hearing-impaired or not, in improving hearing response for applications other than speech recognition. In particular, music enjoyment would be enhanced with a high-fidelity audiometric process that measures hearing acuity for many frequencies, and that can track changes over time and compensate for them. Furthermore, most audiometric results (as limited as they tend to be) are applied only for the tuning of hearing aids or dedicated devices, such as that disclosed in U.S. Pat. No. 7,564,979. Many people of advancing age continue to enjoy music using many playback systems, and need a way to adjust the quality of the playback to take into account their particular hearing profile in a rich way.
While hearing aid devices known in the current art do assist those with significant hearing pathology, they have a number of limitations and do not necessarily improve the quality of sound enjoyment for the listener. Many people with known minor hearing loss decline to use standard hearing aids due to embarrassment or due to the work and expense of maintaining and wearing the device. A very small percentage of the population actually benefits from the use of hearing aids. In general only those individuals who already know they suffer from hearing loss seek out an audiologist while a significant percentage of the population may have significant hearing deficits that go undiagnosed. As the “baby boomer” generation ages the percentage of individuals that could benefit from an audio enhancement method will only increase.
Advanced electronic audio sources have become ubiquitous in our society. Home theater sound systems for music, video and gaming are common and audio quality has become increasingly important. Mobile audio devices such as mobile phones, music players (for example, iPods), and car stereo systems have become standard fare for most individuals. Many individuals are not aware that their hearing is compromised for hearing various frequencies at various volumes. While some devices are equipped with manually regulated equalizers that can be adjusted by an individual to subjectively improve the sound, many are not, and most individuals never take the time to try to adjust standard equalizer settings. Standard equalizer settings are also (like audiograms) very limited as to the number of frequencies that can be adjusted so that their ability to improve the listening experience for an individual is limited. Moreover, while many devices have built-in equalizers (and there are some standalone equalizers available), only sound output coupled to any given equalizer benefits from the settings made by a user. When the same user uses a different piece of equipment, a completely new set of equalizer settings need to be entered. One means common in the art for simplifying the use of equalizers is to provide a plurality of pre-set equalizer adjustments, such as “Bass Reducer”, “Bass Booster”, “Classical”, or “Acoustic”. A shortcoming of these standard settings is that they do not account for, or compensate for, differences in hearing acuity among various individuals.
Audiophiles are individuals whose hobby is to seek high quality audio reproduction and are willing to seek out and pay for high-end audio electronics that come as close to possible to mimicking a live performance. An audiophile may or may not have specific hearing loss. These individuals with an acute sense of quality sound would also provide a market for any device that could custom equalize sound output for a plurality of devices in order to maximize their hearing enjoyment.